Allergy lab tests

Both measure the same thing — allergen-specific IgE — by different routes. Skin-prick testing gives results in minutes but requires stopping antihistamines for several days, intact skin at the test site and a clinic visit; a blood test needs none of that and can be ordered without an allergist appointment, which is why it is the practical first step for most adults. Accuracy is broadly comparable for common inhalant and food allergens. The blood test's weakness is the same as the skin test's: it detects sensitization, not necessarily clinical allergy, so results are always read with your history.

Where blood testing is clearly better: people on daily antihistamines or certain antidepressants, widespread eczema or dermatographism, a history of severe reactions where skin exposure is risky, and infants or anyone who cannot sit for a prick test.

Each allergen is reported as a specific IgE level, usually in kU/L, and a class from 0 to 6. Class 0 means no detectable antibody; classes 1–2 are low and often not clinically meaningful; higher classes make a true allergy more likely. The level correlates with the probability of reacting, not with how severe a reaction would be — a modest level can still produce anaphylaxis in a sensitized person, and a high level in someone who eats the food without symptoms is tolerance, not allergy.

Because positives without symptoms are common — particularly on broad food panels — testing is most useful when it is aimed at what you have actually reacted to. A positive you were not expecting is a reason to talk to your clinician before removing a food, not a diagnosis on its own; unnecessary elimination diets carry their own costs.

IgE panels are the allergy tests: they identify the antibody that causes immediate, sometimes dangerous reactions. IgG food panels measure a different antibody that rises with ordinary exposure to a food; allergy societies do not consider IgG a test for allergy or intolerance, and a long list of IgG “reactive” foods mostly reflects what you eat. We list IgG panels for people who want that exposure data; if your question is “am I allergic?”, the IgE tests above are the ones that answer it.